The present application is directed to surgical instruments for applying a rotational force to an element and, more particularly, to a surgical instrument with a planetary gear system.
Various types of structural elements are used in patients during surgical procedures. Examples include but are not limited to rods such as for attaching to vertebral members or to a broken femur, bone anchors for attaching an elongated element to a bone, pins for attaching together bones or bone sections, and posts for attaching to bones and/or tissue. It is often necessary to remove sections of the structural elements, such as a head of a set screw or an excess length of a rod. Many times the removal occurs after the structural elements have been inserted into a patient. Various instruments are presently used for removing the excess sections. However, the instruments have various drawbacks that add complexity to the surgical procedure.
Some of the previous instruments have a relatively large size. The large size is necessary to generate an adequate force to remove the excess section from the remainder of the structural member. One example is an instrument with large lever arms. The large lever arms are necessary for the instrument to create an adequate shearing force, but the large sizes make the instruments difficult to use in small surgical sites. Further, the instruments may be too large to reach the needed area within the surgical site where the section is to be removed from the remainder of the structural member.
Other instruments are uncontrollable at the time the section is removed. This is caused by the relatively large force necessary to remove the section and the release of the force at the moment of removal. The force release may cause the instruments to “jump” or “buck” making it difficult to control for the medical practitioner. The force release may also cause a shock to the patient.